mailbox: imx: use device name in interrupt name

There are several MUs for different usage, SCMI MU, ELE MU, RemotePROC
MU. Using "imx_mu_chan" in interrupt name would be hard to identify
which MU triggers interrupt, so use device name to make it easy to know
which MU triggers which interrupt.

Signed-off-by: Peng Fan <peng.fan@nxp.com>
Signed-off-by: Jassi Brar <jassisinghbrar@gmail.com>